1. Technical Field
The present invention relates to a semiconductor device, and in particular to a semiconductor having an inductor.
2. Related Art
Mixed mounting of active elements such as MOS transistors and passive elements such as inductors on a semiconductor substrate may raise a problem of noises influential among devices. Japanese Laid-Open Patent Publication 2005-86084 and U.S. Pat. No. 5,936,299 disclose configurations respectively provided with a guard ring which is configured by an impurity diffused layer formed by implanting a P-type or N-type impurity into a semiconductor substrate so as to surround an inductor, aiming at preventing characteristics of the inductor from being affected by noises generated from other circuit elements such as MOS transistor.
There is also known a technique of reducing parasitic capacitance between the inductor and the semiconductor substrate, by suppressing eddy current generated in the substrate while being affected by the inductor.
Japanese Laid-Open Patent Publication 2003-133431 describes a configuration such that an insulating interlayer is locally buried in a surficial portion of a semiconductor substrate, a CMOS is formed in a region having no insulating interlayer provided thereto, and the inductor is provided to a region over the insulating interlayer while being corresponded thereto. Japanese Laid-Open Patent Publication 2001-352039 describes a configuration containing a region having transistors (Q31, Q32) formed therein and a region having an insulating interlayer formed therein, and having an inductor provided over the region having the insulating interlayer formed therein. Japanese Laid-Open Patent Publication No. H11-274412 describes a configuration having an inductor formed over the surface of an insulating material filling up a trench.
The present inventors have recognized as follows. The conventional guard ring has been formed only up to a level of height of a first interconnect layer. For this reason, for the case where the inductor was formed in the upper layer of a multi-layer structure, a problem of causing electromagnetic influences exerted through the lateral space of the inductor may still remain. Therefore, there has been still a room for improving noises possibly induced by the inductor in other devices such as other active elements or passive elements, and possibly induced by the other elements in the inductor.